Following diagram shows overall network architecture. [https://fedoraproject.org/ fedoraproject.org] and [http://fedoraproject.org/wiki/Infrastructure/Services admin.fedoraproject.org] are round robin <code>DNS</code> entries. They are populated based on geoip information. For example, for North America they get a pool of servers in North America. Each of those servers in <code>DNS</code> is a proxy server. It accepts connections using <code>Apache</code>. <code>Apache</code> uses <code>HAProxy</code> as a backend, and in turn some(but not all) services use <code>varnish</code> for caching. Requests are replied to from cache if <code>varnish</code> has it cached, otherwise it sends into a backend application server. Many of these are in the main datacenter in phx2 and some are at other sites. The application server processes the request and sends it back.

This shows whats going on in the proxies. Incoming <code>DNS</code> balanced user application requests hits <code>Apache httpd</code> in proxy server. Apache forwards request to <code>HAProxy</code>, which load balances requests over the app servers. Some of them reaches over <code>VPN</code>. An example of external source is [http://www.fedoraproject.org/people/ fedoraproject.org/people/] which is a proxy pass to [http://people.fedoraproject.org/ people.fedoraproject.org] hosted at Duke. In some cases there is also <code>varnish</code> between <code>HAProxy</code> and the app servers to help cache information. Local requests use standard alias in the <code>apache configs</code>.

This is a generic view of how our applications work. Each application may have its own design, but the premise is the same. Incoming requests are load-balanced from proxy server and reaches to appropriate service box. All application servers in the clustered services area must be identical. If an exception is made it must get moved to solo services box. Most solo services will be one-offs or proof of concept(test) services. Most commonly our single point of failure lie in the data layer.

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